Mass spectrometers are used to determine the chemical composition of substances and structures of molecules. Mass spectrometers may comprise an ion source to produce ions (e.g., to produce ionized neutral molecules) as well as a mass analyzer and ion detector. The mass analyzer may be a time-of-flight (TOF) mass analyzer, for example. TOF mass analyzers may be used to record the mass spectra of compounds or mixtures of compounds by measuring the times for molecular and/or fragment ions of those compounds to travel certain distances.
In orthogonal time of flight mass spectrometry instruments, it is sometimes necessary to control the energy of the beam approaching the orthogonal acceleration region. In such cases, the axial energy of the beam may be controlled to ensure that the ions hit the detector after they travel through the free flight region, and to achieve a good resolution. While the vertical position of the ions in the pulser of a time of flight spectrometer can be compensated for using space focusing techniques, the vertical energy leads to turn-around-time issues which cause bad resolution. So typically, in order to achieve high resolution, the beam is “sliced” to eliminate ions with excessive vertical velocity, both up and down. This is done by passing an ion beam through a slit in a plate so that the ions hit the plate and lose their charge.